This invention relates generally to firmware for processor-based systems.
Processor-based systems may use firmware for booting an operating system. Generally, firmware initiates a system using a particular instruction set architecture. For example, a 32 bit Pentium® architecture platform boots in a flat model protected mode using 32 bit callable interfaces in a 4 gigabyte address space.
After booting, the operating system takes control during a stage called run time. The run time system still uses the same instruction set architecture. However, newer systems can support 32 bit or 64 bit instruction set architectures during run time. A number of other instruction set architectures are also available.
An operating system that was booted in a particular 32 bit instruction set architecture has no support for calling back into the 32 bit mode from the kernel during run time. This problem is addressed by one manufacturer by simply prohibiting the kernel from calling back from one instruction set architecture into another instruction set architecture. See BIOS and Kernel Developer's Guide for AMD Athalon™ 64 and AMD Opteron™ Processors, Publication No. 26094, Revision 306, dated September 2003, available from Advanced Micro Devices, Inc., Sunnyvale, Calif. While this certainly overcomes the problem, it does so in a relatively inflexible way.
Thus, there is a need for ways to enable call backs by an operating system kernel to an instruction set architecture different from the one used to boot the system.